Various types of serial communication protocols are used for communication between electronic devices. Some protocols, such as the Serial Peripheral interface (SPI) protocol, are point-to-point protocols between a master and a slave. SPI is used, for example, in microcontrollers, Liquid Crystal Display (LCD) drivers and SD memory cards, to name just a few examples.
Other protocols, such as the Add-Drop Interface (ADI), are synchronous protocols that multiplex time slots of multiple slaves over a common bus. Add and Drop Multiplexers (ADMs) are used, for example, in SDH/SONET networks, as well as in frequency-domain optical networks such as DWDM. ADMs are offered by various manufacturers. One example is the Fujitsu FLM150 ADM.